NOTES FOR A GEOLOGICAL EXCURSION TO CHARNWOOD FOREST, TO EXAMINE THE CENTRAL GROUP OF PLUTONIC ROCKS OF ENGLAND; AND THE CARBONIFEROUS AND CAMBRIAN STRATA, THROUGH WHICH THEY HAVE BEEN ERUPTED.

In the central county of our Island, within a hundred miles of the Tertiary deposits of the South-east of England, a group of plutonic rocks emerges from beneath the strata of limestone, coal, and red marl which constitute the principal geological features of the midland provinces, and rises up into the bold and picturesque range of hills of Charnwood Forest. Almost the entire series of British rocks is now brought by the railroads within a few hours distance of the metropolis; and the geological inquirer may, in the course of a fortnight, examine in their natural situations the Eocene deposits of the London and Hampshire basins—the Cretaceous and Wealden strata of Sussex, Kent, and Surrey—the Oolitic, Liassic, Triassic, Permian, and Carboniferous systems—the Mountain limestone and its metalliferous treasures—Traps, or ancient lavas, and their effects—strata of the Silurian and Cambrian systems—and, lastly, Granite, Syenite, Porphyry, and other modifications of the plutonic or igneous rocks. The present notes refer to two or three days spent in exploring the country around Leicester, and in examining the granite of Mount Sorel[815]—the slate quarries of Swithland—the syenitic crags of Bardon Hill—the porphyritic masses of Markfield and Grooby—and the coal-mines of Whitwick. On our previous excursion by railway to Leicester (see Excursion to Matlock, p. 867), the order of the succession of the strata from the metropolis to that town was described; on this occasion it will only be requisite to direct the traveller’s attention to the abrupt isolated hills, by Hinckley, Grooby, and the craggy peaks of Charnwood Forest, in the distance, on the left of the railroad, before reaching Leicester. If a pedestrian excursion be resolved upon, three or four days at least will be required to follow the route presently pointed out; in a carriage and pair, it may be accomplished in a long summer s day, by starting from Leicester at six, and returning by ten or eleven.[816]

The geological localities to be visited in this excursion are the following—

I. Barrow-on-Soar.[817] Lias limestone.—The quarries at this locality are celebrated for the organic remains that have from time to time been obtained from the limestone. Bones of Ichthyosauri and Plesiosauri (see p. 669), fishes (Dapedius, p. 603), leaves of cycadeÆ, and fossil wood, together with ammonites, terebratulÆ, &c. may generally be obtained.

Although at the very foot of the plutonic rocks, and on the verge of the grand focus of volcanic action which erupted the syenitic masses of Charnwood Forest, the strata in this spot appear to have suffered but little disturbance. But this phenomenon is in accordance with what occurs in other volcanic districts. For, as M. Constant Prevost remarks, volcanoes may open across all the strata, without occasioning great derangements; thus, at Limagne, Aurillac, and Puy (see Wond. p. 269), the tertiary strata have preserved their horizontality, even around the vents through which issued the volcanic matter that covered those countries with numerous cones of eruption.

II. Mount Sorel. Granite and Syenite.—The road from Leicester ascends a ridge of Triassic or New Red strata, called Birstal Hill, from whence there is a fine view of the town. In the meadows on the left, some ruined walls, covered with ivy, mark the site, and are the only remains of the Abbey in which Cardinal Wolsey expired. Approaching Mount Sorel, an abrupt hill, with a mill on the summit, denotes, from a considerable distance, the geological character of the spot. There is a small Inn in the village, where accommodation may be procured. Visit the quarries, and also the establishment of Mr. Jackson, where the granite is worked into pillars, side-boards, &c.[818]

The hill is about 120 feet in height, and 1,400 yards long; and is estimated to contain about two hundred millions of cubic feet of workable granite, above the general level of the district.[819]

III. Swithland. Slate-rocks.—From Mount Sorel proceed to Swithland: as we approach the quarries, the employment of slate for every available purpose, in the footpaths, walls of cottages, &c., indicates the abundance of this material in the neighbourhood. At Swithland, the quarries are very extensive, and expose magnificent sections, from 100 to 120 feet thick, of strata of Slate, highly inclined; and forming one side of an anticlinal axis, the summit of which will be passed over in our route by Woodhouse. In one quarry, at the time of my visit, a series of nearly horizontal strata of red marl was exposed, lying unconformably upon the edges of the highly inclined beds of Slate. The Slate-rocks of Charnwood Forest have a single anticlinal axis, which strikes from NN.W. to SS.E.; and the axis of the adjacent coal-field of Nuneaton has a similar direction.[820]

IV. Woodhouse. Slate-rocks.—From Swithland to Woodhouse, is a continuation of the highly inclined Slate strata. The village is romantically situated on the ridge or crest of the anticlinal axis of Charnwood Forest. On the sides of the road, there are occasional openings where the strata are exposed. There is, in particular, a fine section on the sides of the elevated point on which the church and school are built, lying to the left of the road in the approach from Swithland. A day might be well spent in this place, and at Swithland.

V. Bardon Hill. Syenite.—We next proceed to Bardon Hill, ascending to the highest ridge of the protruded mass of igneous rock, of which this mountain-range is composed. The craggy and bare pinnacles which are every where presenting themselves, shooting up, as it were, from the green sward, cannot fail, from their novel and striking character, strongly to impress the mind of the young geologist, who now, for the first time, visits a region of plutonic rocks. The view from the summit of the hill is grand and imposing; it should be studied with a geological map of the country before us, that the position of this central mass of volcanic rocks, and its relation to the surrounding sedimentary strata, may be fully comprehended.

VI. Whitwick and Snibstone. Coal-measures.—Spread around the foot of the Syenitic mountain which we are descending are the coal-bearing strata of the Carboniferous system; and in the works at Whitwick and Snibstone the geological inquirer can examine the nature of these deposits in the coal-mines, which he should descend, and obtain specimens of the strata and fossils from the beds in situ.[821]

Among the refuse of the workings thrown up from the various shafts, search should be made for stems of calamites (p. 108), seed-vessels (p. 149), fern-leaves (p. 109), &c.

A section from Whitwick, through Charnwood Forest, to Barrow-on-Soar, in the direction of the route we have traversed, would give the following succession of rocks:—1. Whitwick; Coal-strata, highly inclined. 2. Slate-rocks of Woodhouse, highly inclined. 3. Protrusions of Syenite. 4. Slate-rocks of Swithland, highly inclined, with unconformable strata of red marl. 5. Granite and Syenite of Mount Sorel. 6. Red marl and sandstone, supporting the Lias, at Barrow-on-Soar.

The pedestrian should spend one or two days at Snibstone, where there is humble, but comfortable accommodation.

VII. Markfield and Grooby. Syenite and Porphyry, &c.—These places may be visited on our way back to Leicester.